Intrusion alarm systems are known for detecting the presence of a moving intruder or target within a zone under protection. An energy pattern, which may be provided from a sonic, ultrasonic or electromagnetic source, is provided in a protected zone and reflected energy returned from the zone and from objects therein is received and processed to indicate intruder presence. In the presence of a moving intruder, a Doppler or other sensible signal is received and usually is processed to discriminate a moving intruder from fixed background return energy, noise or spurious signals. In the event of a system failure it is useful to provide a fail-safe mode of operation in which an alarm indication is provided upon such failure so that prompt corrective action can be taken.
Various test systems have been proposed to monitor the operation of intrusion alarm systems to ascertain a failure condition. In one type of test system, a Doppler test signal is provided at the system receiver, or the transmitter is modulated with a Doppler signal to provide a corresponding Doppler signal at the receiver, to cause a system alarm indication in the presence of such a test signal. The absence of alarm actuation would be indicative of system failure. Such command-type testing is not an on-line procedure and usually requires the presence of a person to conduct the test and monitor the expected alarm which should appear at test time. In known on-line testing approaches, the transmitter output signal is monitored and the noise level of the receiver output is also monitored to indicate transmitter and receiver operability. However, such on-line testing does not provide a test of overall system operability to assure detection by the system of an intruder.